Method for operating a selective stiffening catheter

ABSTRACT

A method for delivering RF energy to living tissue includes the steps of extending a guidewire to a tissue treatment site in a body. A controllable stiffness catheter is provided with a stiffness device having non-metallic properties and a temperature-changing device. The stiffness device is in a stiff state below a given temperature and in a soft state above the given temperature. While supplying power to the temperature-changing device, the catheter is threaded along the guidewire up to the treatment site in the soft state. Power is removed from the temperature-changing device to alter the non-metallic properties of the stiffness device and directly result in a change of the stiffness device to the stiff state without straightening the catheter. The RF energy supply device is physically contacted with the treatment site and RF energy is delivered to the treatment site from the RF energy supply device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is:

-   -   a divisional of U.S. patent application Ser. No. 11/395,903,        filed Mar. 31, 2006, and entitled “Method for Operating a        Selective Stiffening Catheter;” and    -   a continuation-in-part of U.S. patent application Ser. No.        11/233,993, filed Sep. 23, 2005, and entitled “Catheter with        Controllable Stiffness and Method for Operating a Selective        Stiffening Catheter” (which application claims the priority,        under 35 U.S.C. §119, of U.S. Provisional Patent Application No.        60/612,684 filed Sep. 24, 2004),        the entire disclosures of which are hereby incorporated herein        by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The invention lies in the field of medical devices, namely, catheters.In particular, the invention relates to catheters that can changestiffness characteristics in use and their uses.

BACKGROUND OF THE INVENTION

To gain access to treatment sites in the body, catheters must beflexible enough to conform to and follow natural anatomical pathways asthey are advanced. These pathways can be quite tortuous, made of softand delicate tissues with many twists and turns. In the vasculature,this is especially the case, and even more so in certain areas of thevasculature such as the vessels of the brain and the coronary arteries.

When treating a site in the vasculature, the state-of-the-art practiceis to first gain access to the treatment site with a flexible, steerableguidewire. Such a guidewire can be precisely controlled by the physicianand steered into place using radiographic guidance. Once the guidewireis in-place, the catheter is advanced over the guidewire. The cathetermust be flexible enough to smoothly follow the pathway of guidewire. Thecatheter can, then, be used to deliver the treatment.

In the case of arterial blockage, the catheter may be a balloondilatation catheter that is used to open the blockage. The guidewire is,first, passed beyond the lesion, and the catheter is advanced over theguidewire and through the lesion. In the case of complete or nearlycomplete blockage, the force required to advance the guidewire throughthe lesion can be difficult for the physician to generate by pushing onthe flexible guidewire from the arterial access site. Further, thisaccess site may be far from the treatment site, such as in the case ofcoronary arterial treatment where access to the coronary arteries isgained though the femoral artery. In such a situation, the physician istrying to advance the flexible guidewire through an obstruction over 100cm away from where he/she is pushing. The same flexibility that helpedgain access to the treatment site now inhibits the advancement of theguidewire. The guidewire bends and buckles under the strain and verylittle thrust is delivered to the tip of the guidewire.

Current practice advances the balloon catheter up to the treatment siteto provide support to the guidewire as it is advanced through thelesion. This is an improvement, but the catheter is also very flexibleand provides little if any additional support. Specialty supportcatheters, which offer more support than balloon catheters, are alsoused. These provide an improvement over balloon catheters but are alsolimited by how flexible they must be to reach the treatment site.

The above-mentioned problems are compounded in the case of a totalarterial blockage or Chronic Total Occlusion (CTO). Accordingly, mostCTOs go untreated. And, there is no catheter-based standard acceptedpractice for CTO treatment. Currently, treatment of CTOs by catheterinterventionalists is performed by attempting to pass a guidewire acrossthe CTO. Once the guidewire is across, a low profile balloon cathetercan be advanced over the guidewire to dilate the lesion. Such aprocedure is almost always followed by placement of a stent. Specialtyguidewires are available to aid the physician in this effort but they,too, are limited in their utility by the constraints of flexibility andcompliance. It is noted that attempting to cross CTOs is a tediouspractice with current equipment and is met with limited success.

Atrial fibrillation is the most common heart arrhythmia in the world,affecting over 2.5 million people in the United States alone. In atrialfibrillation, the electrical signals in the atrial (upper) chambers ofthe heart are chaotic. In addition, the atrial electrical impulses thatreach the ventricles (lower heart chambers) often arrive at irregularintervals.

Ablation of cardiac tissue, to create scar tissue that poses aninterruption in the path of the errant electrical impulses in the hearttissue, is a commonly performed procedure to treat cardiac arrhythmias.Such ablation may range from the ablation of a small area of hearttissue to a series of ablations forming a strategic placement ofincisions in both atria to stop the conduction and formation of errantimpulses.

Ablation has been achieved or suggested using a variety of techniques,such as freezing through cryogenic probe, heating through RF energy,surgical cutting, and other techniques. As used here, “ablation” meansthe removal or destruction of the function of a body part, such ascardiac tissue, regardless of the apparatus or process used to carry outthe ablation. Also, as used herein, “transmural” means through the wallor thickness, such as through the wall or thickness of a hollow organ orvessel.

Ablation of cardiac tissue may be carried out in an open surgicalprocedure, where the breastbone is divided and the surgeon has directaccess to the heart, or through a minimally invasive route, such asbetween the ribs or through a catheter that is introduced through a veinand into the heart. Types of ablation for atrial fibrillation includePulmonary vein isolation ablation (PVI Ablation or PVA), cryoablation(freezing), and atrioventricular (AV) node ablation with pacemakers.

Prior to any ablation, the heart typically is electronically mapped tolocate the point or points of tissue that are causing the arrhythmia.With minimally invasive procedures such as through a catheter, thecatheter is directed to the aberrant tissue, and an electrode orcryogenic probe is placed in contact with the endocardial tissue. RFenergy is delivered from the electrode to the tissue to heat and ablatethe tissue (or the tissue may be frozen by the cryogenic probe), thuseliminating the source of the arrhythmia.

Common problems encountered in this procedure are difficulty inprecisely locating the aberrant tissue, and complications related to theablation of the tissue. Locating the area of tissue causing thearrhythmia often involves several hours of electrically “mapping” theinner surface of the heart using a variety of mapping catheters, andonce the aberrant tissue is located, it is often difficult to positionthe catheter and the associated electrode or probe so that it is incontact with the desired tissue.

The application of either RF energy or ultra-low temperature freezing tothe inside of the heart chamber also carries several risks anddifficulties. It is very difficult to determine how much of the catheterelectrode or cryogenic probe surface is in contact with the tissue sincecatheter electrodes and probes are cylindrical and the heart tissuecannot be visualized clearly with existing fluoroscopic technology.Further, because of the cylindrical shape, some of the exposed electrodeor probe area will almost always be in contact with blood circulating inthe heart, giving rise to a risk of clot formation.

Clot formation is almost always associated with RF energy or cryogenicdelivery inside the heart because it is difficult to prevent the bloodfrom being exposed to the electrode or probe surface. Some of the RFcurrent flows through the blood between the electrode and the hearttissue and this blood is coagulated, or frozen when a cryogenic probe isused, possibly resulting in clot formation. When RF energy is applied,the temperature of the electrode is typically monitored so as to notexceed a preset level, but temperatures necessary to achieve tissueablation almost always result in blood coagulum forming on theelectrode.

Overheating or overcooling of tissue is also a major complication,because the temperature monitoring only gives the temperature of theelectrode or probe, which is, respectively, being cooled or warmed onthe outside by blood flow. The actual temperature of the tissue beingablated by the electrode or probe is usually considerably higher orlower than the electrode or probe temperature, and this can result inoverheating, or even charring, of the tissue in the case of an RFelectrode, or freezing of too much tissue by a cryogenic probe.Overheated or charred tissue can act as a locus for thrombus and clotformation, and over freezing can destroy more tissue than necessary. Itis also very difficult to achieve ablation of tissue deep within theheart wall.

Other forms of energy have been used in ablation procedures, includingultrasound, cryogenic ablation, and microwave technology. When used froman endocardial approach, the limitations of all energy-based ablationtechnologies to date are the difficulty in achieving continuoustransmural lesions and minimizing unnecessary damage to endocardialtissue. Ultrasonic and RF energy endocardial balloon technology has beendeveloped to create circumferential lesions around the individualpulmonary veins. See e.g., U.S. Pat. No. 6,024,740 to Lesh et al. andU.S. Pat. Nos. 5,938,660 and 5,814,028 to Swartz et al. However, thistechnology creates rather wide (greater than 5 mm) lesions that couldlead to stenosis (narrowing) of the pulmonary veins. The large lesionarea can also act as a locus point for thrombus formation. Additionally,there is no feedback to determine when full transmural ablation has beenachieved. Cryogenic ablation has been attempted both endocardially andepicardially (see e.g., U.S. Pat. No. 5,733,280 to Avitall, U.S. Pat.No. 5,147,355 to Friedman et al., and U.S. Pat. No. 5,423,807 to Milder,and WO 98/17187, the latter disclosing an angled cryogenic probe, onearm of which is inserted into the interior of the heart through anopening in the heart wall that is hemostatically sealed around the armby a suture or staples), but because of the time required to freezetissue, and the delivery systems used, it is difficult to create acontinuous line, and uniform transmurality is difficult to verify.

International Publications W099/56644 and W099/56648 disclose anendocardial ablation catheter with a reference plate located on theepicardium to act as an indifferent electrode or backplate that ismaintained at the reference level of the generator. Current flows eitherbetween the electrodes located on the catheter, or between theelectrodes and the reference plate. It is important to note that thisreference plate is essentially a monopolar reference pad. Consequently,there is no energy delivered at the backplate/tissue interface intendedto ablate tissue. Instead, the energy is delivered at theelectrode/tissue interface within the endocardium, and travels throughthe heart tissue either to another endocardial electrode, or to thebackplate. Tissue ablation proceeds from the electrodes in contact withthe endocardium outward to the epicardium. Other references discloseepicardial multi-electrode devices that deliver either monopolar orbipolar energy to the outside surface of the heart.

It is important to note that all endocardial ablation devices thatattempt to ablate tissue through the full thickness of the cardiac wallhave a risk associated with damaging structures within or on the outersurface of the cardiac wall. As an example, if a catheter is deliveringenergy from the inside of the atrium to the outside, and a coronaryartery, the esophagus, or other critical structure is in contact withthe atrial wall, the structure can be damaged by the transfer of energyfrom within the heart to the structure. The coronary arteries,esophagus, aorta, pulmonary veins, and pulmonary artery are allstructures that are in contact with the outer wall of the atrium, andcould be damaged by energy transmitted through the atrial wall.

Therefore, it would be beneficial to provide a catheter that can advanceup to the treatment site with sufficient flexibility through a tortuouspath and that can provide sufficient support to advance through a CTOlesion.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a catheter withcontrollable stiffness and method for operating a selective stiffeningcatheter that overcome the hereinafore-mentioned disadvantages of theheretofore-known devices and methods of this general type and that cantraverse a natural passage of the body in a first flexible state and canbe made to change to a second stiffer state and cycle back and forthrepeatedly between these states at will and that can traverse tortuousanatomy by conforming to it and, once in-place, can be made to stiffenand maintain its tortuous shape in the anatomy.

The catheter of the present invention provides a platform on whichphysicians can deliver tools to treatment sites to aid in the crossingof arterial blockages, especially, CTOs. In the stiff state, these toolscan be used and the force applied by the tools on the treatment site canbe enhanced and increased based upon the stiffness properties of thecatheter.

The catheter according to the invention has a stiffness that can becontrolled during use. The stiffness of the catheter can be changedduring use from soft and flexible to firm and stiff, and back again, ifdesired. The entire length of the catheter can be made to change itsstiffness characteristics. Alternatively, and/or additionally, anyportion or portions of the device can be configured to change itsstiffness characteristics as well.

The catheter is delivered to the treatment site in the flexible state,in which, it will track over the guidewire and conform to the anatomicalpathway, e.g., the vasculature. Once in-place, the catheter can be madeto become stiff (either in whole or in part) without straightening and,thereby, maintain its conformance to the vasculature. In such a state,the catheter provides a stiff conduit to deliver tools to the treatmentsite without compromising the natural anatomy. This stiffness providesthe support necessary to efficiently advance the guide or crossing wireswithout loss of motion and efficiently transmit thrust loads to thetools.

In the case of a guidewire as described above, the guidewire will, withuse of the catheter according to the invention, not flex away from thetreatment site when pushed and provides great increases in feel,control, and thrust. Such characteristics aid in the successful crossingof difficult-to-cross lesions and provide an opportunity to cross CTOs.

The vasculature example above has been used to describe the problem andembodiments of the present invention, but it can be appreciated thatthis same concept can be used in any part of the body.

With the foregoing and other objects in view, there is provided, inaccordance with the invention, a method for delivering radiofrequency(RF) energy to living tissue. A guidewire is extended to a tissuetreatment site in a body. A controllable stiffness catheter is providedand has a shaft having a distal end, a stiffness sheath, and an accesslumen, a stiffness device disposed at the stiffness sheath, havingnon-metallic properties, and being in a relatively stiff state at orbelow a first temperature and being in a relatively soft state at orabove a second temperature, the relatively soft state being entered inresponse to a change in the non-metallic properties of the stiffnessdevice, a temperature-changing device in thermal contact with thestiffness device, the temperature-changing device changing a temperatureof the stiffness device at least below the first temperature and abovethe second temperature, a power controller electrically connected to thestiffness device and selectively supplying power to thetemperature-changing device to change a stiffness of the stiffnessdevice between the stiff state and the soft state, and an RF energysupply device having at least a portion thereof disposed at the distalend of the shaft for selectively supplying RF energy from the distalend. While supplying power to the temperature-changing device, thecontrollable stiffness catheter is threaded along the guidewire up tothe treatment site. Power is removed from the temperature-changingdevice to alter the non-metallic properties of the stiffness device anddirectly result in a change of stiffness of the stiffness device to thestiff state without straightening the catheter. The RF energy supplydevice physically contacts the treatment site and RF energy is deliveredto the treatment site from the RF energy supply device.

In accordance with another mode of the invention, there is also providedthe step of gaining access to the treatment site with the guidewire bysteering the guidewire into place using radiographic guidance.

In accordance with a further mode of the invention, there are alsoprovided the steps of placing the catheter into the relatively flexiblestate by changing a temperature of the stiffness device with thetemperature-changing device to at least approximately 115° F. andplacing the catheter into the relatively stiff state by changing atemperature of the stiffness device with the temperature-changing deviceto approximately body temperature.

With the objects of the invention in view, there is also provided amethod for operating a controllable stiffness catheter to treat atrialfibrillation. A controllable stiffness catheter is provided and has ashaft having a distal end, a stiffness sheath, and an access lumen, aheater inside the stiffness sheath, a non-metallic binder filling thestiffness sheath containing the heater to at least partially surroundand thermally contact the heater, the non-metallic binder beingrelatively solid at or below body temperature and at least partiallymelting and relatively softened above body temperature, the shaft beingin a relatively stiff state when the binder is at or below bodytemperature and in a relatively flexible state when above bodytemperature, a power connection selectively supplying power to theheater to change a stiffness of the shaft between the relatively stiffstate when the heater is not powered and the relatively flexible statewhen the heater is powered, and a radiofrequency (RF) energy supplydevice having at least a portion disposed at the distal end of the shaftfor selectively supplying RF energy from the distal end. Power isapplied to the heater to place the shaft in the relatively flexiblestate. The shaft traverses a passage of a body in the relativelyflexible state to deliver the distal end of the catheter to a cardiactissue treatment site and to physically contact the RF energy supplydevice with the treatment site. Power is removed from the heater toplace the catheter into the relatively stiff state and to substantiallymaintain a current shape of the shaft in the body and at least a portionof the distal end in contact with the treatment site and RF energy isdelivered to the treatment site from the RF energy supply device.

In accordance with an added mode of the invention, there are providedthe steps of placing the catheter into the relatively flexible state bychanging a temperature of the heater to a first temperature and placingthe catheter into the relatively stiff state by changing a temperatureof the heater to a second temperature different from the firsttemperature.

In accordance with an additional mode of the invention, the firsttemperature is higher than the second temperature.

In accordance with yet another mode of the invention, the secondtemperature is approximately at body temperature and the firsttemperature is at least 10 degrees Fahrenheit greater than the secondtemperature.

In accordance with yet a further mode of the invention, the secondtemperature is approximately 105° F. and the first temperature is atleast approximately 115° F.

With the objects of the invention in view, there is also provided amethod for delivering a selectively articulated catheter to a treatmentsite. A guidewire is extended to a treatment site in a body. Acontrollable articulation catheter is provided and has a shaft having astiffness sheath and an access lumen, an articulation control devicedisposed at the stiffness sheath and being in a non-articulating stateat or below a first temperature and being in an articulating state at orabove a second temperature, the articulation control device having anon-metallic binder that is at least partially melted during thearticulating state, a temperature-changing device in thermal contactwith the articulation control device, the temperature-changing devicechanging a temperature of the articulation control device at least frombelow the first temperature to above the second temperature, and a powercontroller electrically connected to the articulation control device andselectively supplying power to the temperature-changing device to changea stiffness of the articulation control device between thenon-articulating state and the articulating state. While supplying powerto the temperature-changing device to place the articulation controldevice in the articulating state, the catheter is threaded along theguidewire up to the treatment site and is pressed adjacent the treatmentsite to articulate the shaft into at least one of a desired shape and adesired orientation. Power is removed from the temperature-changingdevice to place the articulation control device in the non-articulatingstate without straightening the shaft and, thereby, substantiallymaintain at least one of the desired shape and the orientation of theshaft.

In accordance with again another mode of the invention, with thecatheter in the non-articulating state, the guidewire is distallyextended through the treatment site to create a breach at the treatmentsite.

In accordance with again a further mode of the invention, there areprovided the steps of withdrawing the catheter from the guidewire whileleaving the guidewire in the breach and advancing a second prosthesisimplanting catheter different from the catheter over the guidewire andthrough the breach to implant a prosthesis at the treatment site.

In accordance with again an added mode of the invention, the secondprosthesis implanting catheter is a balloon expanding catheter and theprosthesis is a stent surrounding a balloon, and which further comprisesexpanding the balloon to dilate the treatment site and place the stentwithin the dilated breach.

In accordance with again an additional mode of the invention, the secondprosthesis implanting catheter is a sheath delivery catheter and theprosthesis is a stent compressed within a sheath of the sheath deliverycatheter, and which further comprises withdrawing the sheath to permitexpansion of the stent and dilation of the breach.

In accordance with still another mode of the invention, the treatmentsite is a Chronic Total Occlusion.

In accordance with still a further mode of the invention, with thecatheter in the non-articulating state, the guidewire is entirelyremoved and replaced with a breaching tool and the breaching tool isdistally extended through the treatment site to create a breach at thetreatment site.

In accordance with still an added mode of the invention, with thecatheter in the non-articulating state, a tool is slid distally over thecatheter at a proximal end of the catheter and extending the tool overthe catheter to the treatment site.

In accordance with still an additional mode of the invention, at least aportion of a radiofrequency (RF) energy device is provided at a distalend of the catheter for selectively supplying RF energy from the distalend and, after placing the catheter into the non-articulating state, theRF energy device physically contacts the treatment site and RF energy isdelivered to the treatment site from the RF energy device.

In accordance with another mode of the invention, after placing thecatheter into the non-articulating state, a radiofrequency (RF) energydevice traverses to a distal end of the catheter for selectivelysupplying RF energy from the distal end and RF energy is delivered tothe treatment site from the RF energy device.

In accordance with a further mode of the invention, after placing thecatheter into the non-articulating state, the guidewire is removed toempty the guidewire lumen, a radiofrequency (RF) energy device traversesto a distal end of the catheter for selectively supplying RF energy fromthe distal end, the RF energy device physically contacts the treatmentsite, and RF energy is delivered to the treatment site from the RFenergy device.

In accordance with an added mode of the invention, before placing thecatheter into the non-articulating state, a radiofrequency (RF) energydevice traverse to a distal end of the catheter for selectivelysupplying RF energy from the distal end and, after placing the catheterinto the non-articulating state, RF energy is delivered to the treatmentsite from the RF energy device.

In accordance with a concomitant mode of the invention, before placingthe catheter into the non-articulating state, the guidewire is removedto empty the guidewire lumen and a radiofrequency (RF) energy devicetraverses through the guidewire lumen to a distal end of the catheterfor selectively supplying RF energy from the distal end and, afterplacing the catheter into the non-articulating state, the RF energydevice physically contacts the treatment site and RF energy is deliveredto the treatment site from the RF energy device.

Other features that are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a catheter with controllable stiffness and method for operating aselective stiffening catheter, it is, nevertheless, not intended to belimited to the details shown because various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof, will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of embodiments the present invention will be apparent fromthe following detailed description of the preferred embodiments thereof,which description should be considered in conjunction with theaccompanying drawings in which:

FIG. 1 is a fragmentary, enlarged perspective view of a distal end of ashaft of a catheter according to the invention;

FIG. 2 is a block and schematic circuit diagram and a diagrammatic sideelevational view of a proximal end of the catheter according to theinvention;

FIG. 3 is a fragmentary, enlarged, cut-away, perspective view of adistal end an alternative embodiment of the catheter according to theinvention;

FIG. 4 is a fragmentary, enlarged, cut-away, perspective view of adistal end a further alternative embodiment of the catheter according tothe invention;

FIG. 5 is a fragmentary, partially cut-away perspective view of a heartwith a variflex catheter according to the invention traversing an aortainto the left ventricle;

FIG. 6 is a fragmentary, partially cut-away perspective view of a heartwith a variflex catheter according to the invention traversing aninferior vena cava into the right atrium;

FIG. 7 is a fragmentary, partially cut-away perspective view of a heartwith a variflex catheter according to the invention traversing aninter-atrial septum to reach the left atrium;

FIG. 8 is a fragmentary, side elevational view of a vena cava filterimplanted in a vessel and containing a variflex portion according to theinvention in a stiff state;

FIG. 9 is a fragmentary, side elevational view of the filter of FIG. 8with the variflex portion in a soft, flexible state;

FIG. 10 is a fragmentary, exploded and partially hidden side elevationalview of a channel with a variflex distal end and a stylette to beinserted in the channel; and

FIG. 11 is a fragmentary, partially hidden side elevational view of anendoscope and an attached channel with a snare device inserted therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the spiritor the scope of the invention. Additionally, well-known elements ofexemplary embodiments of the invention will not be described in detailor will be omitted so as not to obscure the relevant details of theinvention.

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward.

Before the present invention is disclosed and described, it is to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting. It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise.

Referring now to the figures of the drawings in detail and first,particularly to FIG. 1 thereof, there is shown a distal portion of ashaft 10 of an exemplary embodiment of a catheter 1 according to theinvention. The shaft 10 is configured with an outer sheath 11 made of apolymer tube such as polyurethane and an inner sheath 12 made of apolymer tube such as PTFE. The inner sheath 12 is assembledsubstantially concentrically with the outer sheath 11. The annulusbetween the inner and outer sheaths 12, 11 is filled with a stiffnessdevice, in particular, at least one carbon fiber tow 13 (preferably, 2to 4 tows 13 extending longitudinally in a helix or braided) impregnatedwith a binder such as a low-melt-point paraffin or microcrystalline waxor other temperature dependent phase change material. At bodytemperature, the binder is a solid and, therefore, the carbon fiber tow13 behaves substantially as a solid carbon fiber rod. (As used herein,“body temperature” is defined to be approximately 40.5° C. (105° F.) orbelow). In such a condition, the catheter is stiff due the high modulusof the carbon fibers.

It is noted that concentricity is not a requirement. In anotherexemplary embodiment of the catheter 1 of the present invention, theinner sheath 12 can merely be off-center or the inner sheath 12 can bedisposed at the inner wall of the outer sheath 11. In the latterorientation, the space in which the stiffness device resides is somewhatcrescent-shaped.

In one exemplary embodiment, an electrical conductor 14, such asinsulated copper wire, makes electrical contact with the distal end(s)of the carbon fiber tow(s) 13 and runs from the distal end of thecatheter 1 to the proximal end of the catheter 1. The proximal end(s) ofthe carbon fiber tow(s) 13 makes contact with a second electricalconductor 15, such as copper wire, which extends to the proximal end ofthe catheter 1 at which resides a power supply 16 (e.g., a battery or anelectric mains) and a controller 17 as shown in FIG. 2. The proximalends of the two conductors 14, 15 are electrically connected to thepower supply 16 through the controller 17. These features make up asimple electrical circuit with the carbon fiber tow(s) acting like aresistor in the circuit. When voltage is applied to the two electricalconductors 14, 15, current flows through the circuit 13, 14, 15 andresistively heats the carbon fiber tow(s) 13. When the tow 13 is heatedto raise the temperature of the binder above a binder transitiontemperature, the binder softens (which can include a partial or a fullmelt) and allows the individual carbon fibers to move with respect toeach other, thereby making the catheter shaft more flexible than before.(As used herein, the binder transition temperature is at or aboveapproximately 46° C. (115° F.).) When the voltage is removed from thecircuit 13, 14, 15, the binder cools and solidifies. Thus, the cathetershaft 10 stiffens to its then constrained shape. This heating andcooling can be done repeatedly—making the catheter 1 flexible whennavigating through a tortuous path and stiff when placed in a positionfor use, for example.

Another exemplary embodiment of the catheter 1 according to theinvention is similar to that illustrated in FIG. 1 but, instead of aconcentric configuration, the shaft 10 is constructed of a first hollowsheath 11 made of a polymer tube such as polyurethane and a secondhollow sheath 12 made of a polymer tube such as PTFE. The first sheath11 is assembled next to and outside of the interior of the second sheath12 such that a cross-section of the two conduits is shaped like thenumber eight. The entire core of the second sheath 12, therefore, can beused to house the stiffness device 13.

Electrical power for supplying a voltage or current can be provided, forexample, by at least one battery 16. This battery 16 can be connected tothe conductors 14, 15 through the controller 17, which is configured tolimit heating of the binder by limiting current through the circuit 13,14, 15. Such current limiting can be achieved by using aProportional-Integral-Derivative (PID) controller whereby a standardfeedback loop measures the “output” of the process and controls the“input”, with a goal of maintaining the output at a target value, whichis called the “setpoint”. Such a current-sensing controller, forexample, could make the initial current through the circuit 13, 14, 15high enough to achieve a rapid melt and, thus, a rapid softening, with asubsequent decrease and leveling in the current to just maintain themelt. A thermocouple 18 can be added to actively monitor temperature ofthe melt. A control switch 19 and indicator LEDs 20 are added to thehandle of the catheter 1 to give control and feedback to the user.

The entire length of the catheter 1 can be controllable in stiffness orjust a portion of it can be controlled. In the case of a coronarycatheter, the distal 20 cm or so can be controllable. The remainder ofthe catheter 1 can be constructed to have a stiffness sufficient todeliver the controllable portion to the coronary arteries. In such anembodiment, the stiffness device 13 is only present in the distalquarter of the shaft, for example, and one conductor 14 is electricallyconnected to the distal end of the stiffness device 13 (located atapproximately the distal end of the shaft) and the other conductor 15 iselectrically connected to a point on the shaft approximatelythree-quarters of the way to the distal end of the stiffness device 13.

The connection of conductors 14, 15 need not only be at the two ends ofthe stiffness device 13. Additional non-illustrated conductors can beelectrically connected to different places along a single stiffnessdevice 13 that extends the entire length of the catheter 1 to, thereby,subdivide the stiffness device 13 into different stiffening segments.The proximal ends of each of these additionally conductors areelectrically connected to the controller 17. Accordingly, only a portionor a set of portions of the stiffness device 13 can be softeneddepending upon which conductors are energized. Alternatively, thestiffness device 13 can be a set of tows 13 having different lengthswith two conductors connected respectively to each tow.

In any embodiment of the conductors 14, 15 and the stiffness device 13,the conductors should be electrically isolated from one another. Even ifone conductor contacts a first end of all of a plurality of stiffnessdevices 13, the other conductors connected to the second end of eachstiffness device must be electrically isolated from one another and theone conductor contacting the first end.

FIG. 1 shows a plurality of carbon tows 13 and distal conductors 14, 15wound around the inner sheath 12. The pitch and the quantity of thecarbon fiber tows 13, and the properties of the binder, can be adjustedto affect the final stiffness of the catheter 1. A stiffer binder or theaddition of more carbon fiber would lead to a stiffer catheter and aless stiff binder or the subtraction of carbon fiber would lead to aless stiff catheter. A change in the pitch of the wind along the lengthof the catheter 1 would also vary the stiffness along its length.

The carbon fiber tows 13 can also be oriented longitudinally as rodswithout wrapping them around the inner sheath 12. Or, a hollow braid ofthe carbon fiber tows 13 can be made to surround the inner sheath 12.The distal conductor(s) 14, 15 could be included anywhere along the inthe rods or braid if desired.

A luer fitting 21 is located at the proximal end of the catheter 1. Thisfitting 21 provides access to the central lumen of the catheter, forexample, for a CTO-piercing tool. A hemostasis valve can be connected tothe fitting 21, for example, while the catheter is in use.

In another embodiment of the stiffness device, a mixture of shorterdiscontinuous fibers such as chopped carbon fiber or fiberglass andbinder can be used instead of impregnated continuous carbon fiber tows13. In such a case, the fibers would no longer be used as the resistiveheating measure. Heating of the binder can be achieved by wrapping theinner sheath 12 with a resistive heating element, such asNickel/Chromium (e.g., NICHROME®) wire. In such a configuration, thewire passes the current and becomes warm, thus heating the surroundingfiber-loaded binder.

In the case of a coronary version of the catheter, the lumen diameter ofthe inner sheath is, at a minimum, 0.4064 mm (0.016″) to ensure freepassage of 0.3556 mm (0.014″) diameter steerable coronary guidewires. Itis preferred for the outer diameter of the catheter to be no greaterthan 1.651 mm (0.065″) to be compatible with an inner diameter of astandard 6 French coronary guide catheter (minimum inner diameter 1.7272mm (0.068″)). Larger or smaller versions can be constructed to suitspecific needs.

The catheter can also be stiffened using mechanical measures. Theannulus between the inner and outer sheaths can be filled with a finegranular substance, such as aluminum oxide or silica, as shown in FIG.3. In its flexible state, the fine grains are loose and slide past eachother as the catheter is flexed. When vacuum is applied to the annulus,however, the pressure is lowered inside the annulus and the flexibleouter sheath begins to compress the grains of the filler together fromthe urging of the higher pressure outside the catheter. Under suchcompression, the grains are forced against each other and interlock, nolonger sliding past each other and, thus, stiffening the catheterwithout straightening it. The magnitude of the pressure change betweenthe outside of the catheter and the interior of the annulus affects thecatheter stiffness: a small pressure difference (lower vacuum) for amore flexible catheter, a large pressure difference (higher vacuum) fora stiffer catheter. It is clear to see that the catheter could havemultiple independent zones that could each be controlled by a differentlevel of vacuum, thus, illustration of this feature is not necessary tounderstand the present invention. This allows the catheter to be stiffin some zones, and more flexible in others. Such stiffening could alsobe accomplished without using the granular substance by substituting arough surface (such as ridges, grooves, bonded grit and combinationsthereof) on the outside of the inner sheath and on the inside of theouter sheath as shown in FIG. 4. In its flexible state, the two roughsurfaces do not engage each other substantially. When vacuum is applied,the outer sheath is compressed, and the rough surface on the inside ofthe outer sheath begins to engage the rough surface on the outside ofthe inner sheath thereby stiffening the catheter.

The following text outlines exemplary procedures for using the catheter1 of the present invention to pass a CTO.

First, a flexible, steerable guidewire is precisely controlled by thephysician and steered into place at a treatment site in a body using,for example, radiographic guidance. Once the guidewire is in place, thecatheter 1 of the present invention can be advanced over the guidewire.It is understood that body pathways can be quite tortuous and are madeof soft and delicate tissues. This is especially true in thevasculature, in particular, in vessels of the brain and the coronaryarteries. Therefore, using the catheter 1 to gain access to thetreatment site in the body most likely requires that the catheter 1start as being flexible to conform to and follow the natural anatomicalpathways as it is advanced to the site.

In the case of a CTO, the guidewire is advanced only up to the blockage.Then, the access lumen 12 (whether inside the stiffness lumen 11 orouter sheath 11) is threaded on the guidewire. The catheter 1 is in itssoftened state or is caused to enter its softened state so that thecatheter 1 can be threaded along the guidewire up to the CTO. At thepoint where the catheter 1 is near the CTO, the catheter 1 is caused tobecome stiff (without straightening). In the stiff state, a CTO-openingtool will be used to open the CTO. For example, the CTO-opening tool canbe the guidewire itself. Alternatively, a CTO-opening tool can beinserted through the access lumen 12 and into the CTO. If the tool is adevice entirely separate from the catheter 1, the guidewire can beremoved from the catheter 1 and the CTO-opening tool can be threadedthrough the access lumen 12. Preferably, the CTO-opening tool is hard(but flexible to traverse the catheter 1) and has a sharp distal end.

The guidewire or tool is pressed through the CTO with the stiffenedcatheter 1 efficiently transmitting the thrust loads to the tool as theCTO is providing resistance to puncture. Once the guidewire/tool isacross the CTO, the guidewire/tool can be used to guide another devicethat will open and fix the blockage. To remove the catheter 1, first,the catheter 1 is caused to soften. After softening, the catheter 1 isremoved and the guidewire/tool is left in the position passed throughthe CTO. A low profile balloon catheter, for example, is advanced overthe guidewire/tool and through the lesion. The balloon is expanded todilate the lesion. A stent can, then, be placed in the lesion to fix theCTO.

With use of the catheter according to the invention, the guidewire/toolwill not flex away from the treatment site when pushed and providesgreat increases in feel, control, and thrust. Such characteristics aidin the successful crossing of difficult-to-cross lesions and provide anopportunity to cross CTOs.

Atrial fibrillation is the most common heart arrhythmia in the world,affecting over 2.5 million people in the United States alone. In atrialfibrillation, the electrical signals in the atrial (upper) chambers ofthe heart are chaotic. In addition, the atrial electrical impulses thatreach the ventricles (lower heart chambers) often arrive at irregularintervals.

Ablation of cardiac tissue, to create scar tissue that poses aninterruption in the path of the errant electrical impulses in the hearttissue, is a commonly performed procedure to treat cardiac arrhythmias.Such ablation may range from the ablation of a small area of hearttissue to a series of ablations forming a strategic placement ofincisions in both atria to stop the conduction and formation of errantimpulses.

Ablation has been achieved or suggested using a variety of techniques,such as freezing through cryogenic probe, heating through RF energy,surgical cutting, and other techniques. As used here, “ablation” meansthe removal or destruction of the function of a body part, such ascardiac tissue, regardless of the apparatus or process used to carry outthe ablation. Also, as used herein, “transmural” means through the wallor thickness, such as through the wall or thickness of a hollow organ orvessel.

Ablation of cardiac tissue may be carried out in an open surgicalprocedure, where the breastbone is divided and the surgeon has directaccess to the heart, or through a minimally invasive route, such asbetween the ribs or through a catheter that is introduced through a veinand into the heart. Types of ablation for atrial fibrillation includePulmonary vein isolation ablation (PVI Ablation or PVA), cryoablation(freezing), and atrioventricular (AV) node ablation with pacemakers.

Prior to any ablation, the heart typically is electronically mapped tolocate the point or points of tissue that are causing the arrhythmia.With minimally invasive procedures such as through a catheter, thecatheter is directed to the aberrant tissue, and an electrode orcryogenic probe is placed in contact with the endocardial tissue. RFenergy is delivered from the electrode to the tissue to heat and ablatethe tissue (or the tissue may be frozen by the cryogenic probe), thuseliminating the source of the arrhythmia.

Common problems encountered in this procedure are difficulty inprecisely locating the aberrant tissue, and complications related to theablation of the tissue. Locating the area of tissue causing thearrhythmia often involves several hours of electrically “mapping” theinner surface of the heart using a variety of mapping catheters, andonce the aberrant tissue is located, it is often difficult to positionthe catheter and the associated electrode or probe so that it is incontact with the desired tissue.

The application of either RF energy or ultra-low temperature freezing tothe inside of the heart chamber also carries several risks anddifficulties. It is very difficult to determine how much of the catheterelectrode or cryogenic probe surface is in contact with the tissue sincecatheter electrodes and probes are cylindrical and the heart tissuecannot be visualized clearly with existing fluoroscopic technology.Further, because of the cylindrical shape, some of the exposed electrodeor probe area will almost always be in contact with blood circulating inthe heart, giving rise to a risk of clot formation.

Clot formation is almost always associated with RF energy or cryogenicdelivery inside the heart because it is difficult to prevent the bloodfrom being exposed to the electrode or probe surface. Some of the RFcurrent flows through the blood between the electrode and the hearttissue and this blood is coagulated, or frozen when a cryogenic probe isused, possibly resulting in clot formation. When RF energy is applied,the temperature of the electrode is typically monitored so as to notexceed a preset level, but temperatures necessary to achieve tissueablation almost always result in blood coagulum forming on theelectrode.

Overheating or overcooling of tissue is also a major complication,because the temperature monitoring only gives the temperature of theelectrode or probe, which is, respectively, being cooled or warmed onthe outside by blood flow. The actual temperature of the tissue beingablated by the electrode or probe is usually considerably higher orlower than the electrode or probe temperature, and this can result inoverheating, or even charring, of the tissue in the case of an RFelectrode, or freezing of too much tissue by a cryogenic probe.Overheated or charred tissue can act as a locus for thrombus and clotformation, and over freezing can destroy more tissue than necessary. Itis also very difficult to achieve ablation of tissue deep within theheart wall.

Other forms of energy have been used in ablation procedures, includingultrasound, cryogenic ablation, and microwave technology. When used froman endocardial approach, the limitations of all energy-based ablationtechnologies to date are the difficulty in achieving continuoustransmural lesions and minimizing unnecessary damage to endocardialtissue. Ultrasonic and RF energy endocardial balloon technology has beendeveloped to create circumferential lesions around the individualpulmonary veins. See e.g., U.S. Pat. No. 6,024,740 to Lesh et al. andU.S. Pat. Nos. 5,938,660 and 5,814,028 to Swartz et al. However, thistechnology creates rather wide (greater than 5 mm) lesions that couldlead to stenosis (narrowing) of the pulmonary veins. The large lesionarea can also act as a locus point for thrombus formation. Additionally,there is no feedback to determine when full transmural ablation has beenachieved. Cryogenic ablation has been attempted both endocardially andepicardially (see e.g., U.S. Pat. No. 5,733,280 to Avitall, U.S. Pat.No. 5,147,355 to Friedman et al., and U.S. Pat. No. 5,423,807 to Milder,and WO 98/17187, the latter disclosing an angled cryogenic probe, onearm of which is inserted into the interior of the heart through anopening in the heart wall that is hemostatically sealed around the armby a suture or staples), but because of the time required to freezetissue, and the delivery systems used, it is difficult to create acontinuous line, and uniform transmurality is difficult to verify.

International Publications W099/56644 and W099/56648 disclose anendocardial ablation catheter with a reference plate located on theepicardium to act as an indifferent electrode or backplate that ismaintained at the reference level of the generator. Current flows eitherbetween the electrodes located on the catheter, or between theelectrodes and the reference plate. It is important to note that thisreference plate is essentially a monopolar reference pad. Consequently,there is no energy delivered at the backplate/tissue interface intendedto ablate tissue. Instead, the energy is delivered at theelectrode/tissue interface within the endocardium, and travels throughthe heart tissue either to another endocardial electrode, or to thebackplate. Tissue ablation proceeds from the electrodes in contact withthe endocardium outward to the epicardium. Other references discloseepicardial multi-electrode devices that deliver either monopolar orbipolar energy to the outside surface of the heart.

It is important to note that all endocardial ablation devices thatattempt to ablate tissue through the full thickness of the cardiac wallhave a risk associated with damaging structures within or on the outersurface of the cardiac wall. As an example, if a catheter is deliveringenergy from the inside of the atrium to the outside, and a coronaryartery, the esophagus, or other critical structure is in contact withthe atrial wall, the structure can be damaged by the transfer of energyfrom within the heart to the structure. The coronary arteries,esophagus, aorta, pulmonary veins, and pulmonary artery are allstructures that are in contact with the outer wall of the atrium, andcould be damaged by energy transmitted through the atrial wall. CTOcrossing is not the only application for the catheter according to theinvention. Many other uses are possible.

Where treatment of atrial fibrillation requires the delivery ofradiofrequency energy to parts of the heart, the catheter needs to beflexible enough to get to the heart but stiff enough to apply pressureto the heart so that sufficient contact with the tissue is made. If thecontact is not sufficient, then charring can occur at the interfacebetween the device and tissue causing a decrease in the efficacy oftreatment or even injury.

In one exemplary method, the catheter according to the invention can beused to treat atrial fibrillation by delivering the neededradiofrequency energy to parts of the heart. First, a flexible,steerable guidewire is precisely controlled by the physician and steeredinto place at a treatment site in a body using, for example,radiographic guidance. Once the guidewire is in place, the catheter 1 ofthe present invention can be advanced over the guidewire. As set forthabove, using the catheter 1 to gain access to the treatment site in thebody most likely requires that the catheter 1 start as being flexible toconform to and follow the natural anatomical pathways as it is advancedto the site.

In the case of a treatment of atrial fibrillation, the guidewire isadvanced only up to the cardiac tissue to be treated. Then, the accesslumen 12 (whether inside the stiffness lumen 11 or outer sheath 11) isthreaded on the guidewire. The catheter 1 is in its softened state or iscaused to enter its softened state so that the catheter 1 can bethreaded along the guidewire up to the cardiac tissue. At the pointwhere the catheter 1 has contact with the cardiac tissue to be treated,the catheter 1 is caused to become stiff (without straightening). In thestiff state, the portion of the catheter 1 that delivers theradiofrequency energy will be secured at a given contact point.Alignment and contact of the energy imparting area to the cardiac tissueto be treated can be examined and, if satisfactory, the energy can beimparted with increased accuracy to the target tissue. FIGS. 5, 6, and 7illustrate three exemplary applications for use of the catheter intreating atrial fibrillation. FIG. 5 shows a catheter 30 that is guidedthrough the aorta and into the left ventricle. FIG. 6 illustrates thecatheter 30 guided through the inferior vena cava and into the rightatrium. FIG. 7 depicts the catheter 30 passing through a puncture device32 that spans the inter-atrial septum to treat the left atrium. In sucha situation, the variflex technology can be used both on the catheter 30and the puncture device 32.

If the RF energy-delivering tool is a device entirely separate from thecatheter 1, the guidewire can be removed from the catheter 1 and thetool can be threaded through the access lumen 12.

Another exemplary embodiment for the catheter according to the inventionis where passive articulation is required at the distal treatment end ofan atrial fibrillation treatment catheter. Current catheters have activearticulation control for reaching different parts of the heart, but suchcatheters require a cable or cables are pulled at the hand of the usercausing the device to flex at the tip in a predetermined shape. Thevariable flexing (variflex) technology of the catheter according to theinvention could be placed on a portion of the atrial fibrillation (AF)catheter. The AF catheter could be so modified and pushed up againstcardiac tissue with the variflex section in the flexible condition. Thusallowing the physician to bend the variflex section to any desiredposition. When the desired position is reached, the variflex section canbe stiffened. This process could be used for any medical device thatneeded controllable articulation, such as gastro-intestinal (GI)instruments, neurological instruments and other vascular instruments.

Yet another exemplary embodiment for the catheter according to theinvention is for use as a transeptal sheath, which can be articulatedonce it is placed into the atrium of a heart in one of two ways. First,the articulation can occur by the passive articulation that is describedherein. Second, the articulation can be effected by introducing apre-formed, pre-bent stylette. In particular, the transeptal sheath isintroduced into the atrium in the soft, flexible condition. A pre-bentstylette is inserted inside the sheath in a distal direction until thedesired bend of the transeptal sheath inside of the atrium is obtained.The shape of the transeptal sheath is modified by pushing the stylettefurther in the distal direction, by pulling the stylette proximally, orby rotating the stylette. Once the desired shape is obtained, thetranseptal sheath is switched to the stiff condition, thus maintainingthe desired shape.

Still a further exemplary embodiment for the catheter according to theinvention allows use of a removable implant that includes the variflextechnology. The implant has a pre-defined shape for use in the body. Theimplant is caused to become flexible and, therefore, can be reshaped toa configuration that allows implantation and, when at the site in whichit is to be implanted, can be de-energized to harden at the site. Theimplant can be removed from the energy source and left in the body. Inan exemplary embodiment, a spiral variflex stent can be straightened andmoved to the implantation site in a straight configuration. When in adesired position at the implantation site, the stent can be caused tospiral into the shape that prevents migration and opens the vessel. Itwould be left in the implantation position. At a later time, thevariflex energizing system could be reconnected to the implant to makeit flexible again for removal or replacement.

A first medical area that the catheter according to the invention can beuse is cardiovascular. In one application, cardiovascular guidingcatheters can be improved upon by using the variflex technology. Suchvariflex equipped guiding catheters can be inserted into a patient withthe guiding catheter, a section of the guiding catheter, or multiplesections of the guiding catheter using the variflex technology of thepresent invention. Having the variable flexibility makes insertion ofthe guiding catheter into the target vessel easier, increases theback-up support of the guiding catheter, and substantially preventsmigration out of the vessel during use. The guiding catheter is insertedwith the variflex section or sections in the soft state and, then, thevariflex section or sections would be stiffened when the guidingcatheter was placed in the desired position. This would stabilize thetip of the guiding catheter in the target vessel to allow the subsequentpassage of devices thru the guide and into the vessel for treatment.After the procedure is completed, the guide can be made soft again foreasy removal from the vessel.

A second medical area in which the catheter according to the inventioncould be used is with stent delivery systems. For example, such deliverysystems are improved when the variflex technology of the presentinvention is disposed on the inner member of the balloon catheter. Sucha variflex-equipped delivery system still allows easy insertion by usingthe catheter in the soft, flexible state. When the stent is positionedat the desired location, the inner member of the balloon catheter isstiffened to prevent the balloon from migrating during stent deployment,assuring accurate placement of stent in a target lesion.

The invention of the instant application can improve balloon angioplastyas well. Using of the variflex technology permits easier navigationthrough a tortuous vascular system when in the flexible state. Thecatheter delivering the balloon is stiffened and locked in placerelative to the vascular system once the desired location has beenreached. Combined with a balloon/stent viewing system such asfluoroscopy, the stent and/or balloon position can be verified and, ifneeding a different orientation, could be changed by softening andre-hardening the catheter until the desired placement is obtained. Suchan improvement gives the physician more precise control for aligning theballoon with the target lesion.

The variflex invention of the instant application can also improveguidewire technology. In such a configuration, the guidewire has a steelor a Nitinol core and the variflex technology is manufactured around thecore along its entire length, in a particular section, or in multiplesections. The variflex section/sections is/are softened for insertion ofthe guidewire into the patient and are hardened once the guidewire isplaced in its desired position. This orientation locks the guidewire inplace relative to the vascular system.

The variflex invention of the instant application can also improve bloodclot removal technology. For example, a vena cava filter is improvedadding a section 40 of the variflex technology to the arms of the deviceas shown in FIGS. 8 and 9. Such a filter is inserted and left in placewith the variflex section in the hardened condition to give the filterlegs their desired stiffness for springing outward. In such an implantedstate, conventional filters cannot be removed without difficulty orinjury. In comparison, a variflex-equipped vena cava filter can beremoved. First, a catheter equipped to deliver electrical energy to thevariflex section 40 is brought into contact with the filter. Thevariflex section 40 is made to soften and become flexible to allow thearms of the filter to relax. In such a state, easy removal is possible.

A variflex catheter according to the invention can be used inconjunction with reaching tortuous vascular anatomy with a guidewire. Insuch an application, the variflex catheter is loaded over the guidewire.The guidewire is inserted into the patient until it became difficult topass the guidewire. The variflex catheter in its soft condition is,then, inserted over the guidewire close to the guidewire's distal end.The variflex catheter is, then, stiffened and the guidewire is insertedfurther. The variflex catheter supports the guidewire along its length,thus lessening the damage to the vessels and allowing more force to beexerted at the tip of the guidewire.

The variflex invention of the instant application can also be applied tovarious transgastric surgery applications. In one application,illustrated in FIGS. 10 and 11, the variflex technology is used in anendoscopic transgastric surgery where one or more steerable workingchannels 50 having the variable flexibility of the present invention areattached to an endoscope 60 or over the endoscope 60 as an overtube (notillustrated). Such a channel 50 is used to steer devices 70 such assnares, biopsy forceps, graspers, injection needles, etc. The channelembodiment of FIGS. 10 and 11 has a variflex distal portion 52 and anon-variflex proximal portion 54. Of course, any portion of the channel50 can be variflex or not. A stylette 70 with a flexible pre-formedsection at its distal tip is inserted into the working channel 50 withthe variflex section 52 in the soft, flexible state so that the variflexsection 52 takes the shape of stylette 70. The variflex section 52,then, is stiffened. Devices are, then, able to be inserted into theworking channel and through the bent variflex section 52.

The variflex invention of the instant application can also be applied tospinal procedures. For example, spinal fixation rods are used toimmobilize and stabilize segments of the thoracic, lumbar, and sacralspine. Certain acute and chronic spinal disorders may make it necessaryto surgically stabilize the spine using rods and screws. Disorders thatcause spinal instability or deformity include degenerativespondylolisthesis, fractures, scoliosis, kyphosis, spinal tumor, andfailed previous fusion (pseudoarthrosis). The variflex technology of thepresent invention is used with these systems to make adjustments to thepatient's posture after they are implanted. The rods and screws cancontain a section or sections of the variflex technology. The variflexsections are softened to allow for adjustment of the patient's posture.Once the patient's posture is adjusted to the desired position, thevariflex section(s) is/are hardened to maintain the desired posture.

The variflex invention of the instant application can also be applied toextremity immobilization devices. For example, splints, casts, orneckbraces made from sheets of variflex material could be heated(whether with implanted heaters or external heaters such as heat packs)to make the material pliable to be custom fitted to the patient. Afterremoving the heat, the device hardens to provide support to the bodypart. Such configurations are especially desirable in emergencysituations where speed is important, as hardening of the variflexmaterial is extremely fast.

The variflex invention of the instant application can also be applied toendovascular application. For example, when such a catheter or device isused in a contralateral approach during diagnostic and interventionalprocedures, the catheter or device is inserted in its flexible state andis positioned around the bifurcation of the aorta. After the catheter ordevice has been placed in the opposite arm of the bifurcation, it can bestiffened in place to stabilize the catheter or device and allow theuser to advance other devices through or around the device that has thevariflex technology incorporated into one or more segments along itslength.

The variflex invention of the instant application can also be applied toguiding catheters, stent delivery systems, balloon catheters, andsteerable wires as set forth in the cardiovascular applications above.The invention can also be used with neuroradiology procedures. Forexample, in a thrombectomy, devices used to remove blood clots can bemade to perform better by the application of the variflex technology.Specifically, such variable stiffness devices can be incorporated into asmall straight flexible catheter that can be changed into a corkscrewconfiguration at the tip by insertion of a stylette having the desiredshape and, then, stiffening the tip of the catheter to assume the sameconfiguration of the stylette.

The variflex invention of the instant application can also be applied tocoil delivery systems. Incorporation of the variflex technology of thepresent invention into a coil delivery system allows the device to beinserted in its flexible state to a distal location within thevasculature and to be subsequently stiffened to stabilize the deliverysystem in the blood vessel to be treated and to facilitate thedeployment of the coil into the target vessel.

The variflex invention of the instant application can also be applied inthe oncology field. Indwelling venous catheters used for administrationof different chemotherapeuting agents can be stabilized in place afterinsertion using the variflex technology of the present invention.Specifically, it can be used to stiffen the catheter wall and cause thecatheter to assume the shape of the anatomy in which it is placed. Whenit is time to remove the catheter, it can be made flexible for easywithdrawal from the vasculature.

The variflex invention of the instant application can also be applied inthe urology field. For example, Foley catheters can be made more stableand prevent migration by using the variflex technology at the distaltip. The Foley catheter containing a variflex section on the distal endis inserted into the urethra with the variflex section in the soft,flexible condition. Once the variflex section is in the bladder, apreformed stylette (possibly a pigtail) is inserted into the Foleycatheter. The variflex section is, then, hardened to maintain the shapeof the stylette and, therefore, will not migrate. Insertion of astylette with the desired shape, followed by a stiffening of thecatheter, changes the tip of the catheter to a “pigtail” configurationto stabilize the catheter inside the bladder, thus obviating the needfor a balloon. It is noted that a straight, flexible Foley catheter iseasier to insert than the standard curved catheters. Additionally,devices used to treat benign Protatic Hyperplasia can be easier toinsert and deliver to the prostate by the use of the Variflextechnology. Insertion of any device in flexible form followed bysubsequent stiffening facilitates reaching the prostate for treatmentusing dilatation or resection devices.

Exemplary non-medical uses of the variflex technology of the presentinvention include clothes, shoes, boots, and other wearable items thatcould conform to a use's body and, thereafter, be locked in place. Thevariflex technology could be used for body armor that is pliable whenthe person is not in imminent danger. In such a flexible state, thearmor would be comfortable for the user. When the user enters aprecarious situation, the armor is activated to harden for the desiredlevel of protection.

The foregoing description and accompanying drawings illustrate theprinciples, preferred embodiments and modes of operation of theinvention. However, the invention should not be construed as beinglimited to the particular embodiments discussed above. Additionalvariations of the embodiments discussed above will be appreciated bythose skilled in the art.

Therefore, the above-described embodiments should be regarded asillustrative rather than restrictive. Accordingly, it should beappreciated that variations to those embodiments can be made by thoseskilled in the art without departing from the scope of the invention asdefined by the following claims.

We claim:
 1. A method for delivering radiofrequency (RF) energy toliving tissue, which comprises: extending a guidewire to a tissuetreatment site in a body; providing a controllable stiffness catheterhaving: a shaft having a distal end, a stiffness sheath, and an accesslumen; a stiffness device disposed at the stiffness sheath, havingnon-metallic properties, and being in a relatively stiff state at orbelow a first temperature and being in a relatively soft state at orabove a second temperature, the relatively soft state being entered inresponse to a change in the non-metallic properties of the stiffnessdevice; a temperature-changing device in thermal contact with thestiffness device, the temperature-changing device changing a temperatureof the stiffness device at least below the first temperature and abovethe second temperature; a power controller electrically connected to thestiffness device and selectively supplying power to thetemperature-changing device to change a stiffness of the stiffnessdevice between the stiff state and the soft state; and an RF energysupply device having at least a portion thereof disposed at the distalend of the shaft for selectively supplying RF energy from the distalend; while supplying power to the temperature-changing device, threadingthe controllable stiffness catheter along the guidewire up to thetreatment site; removing power from the temperature-changing device toalter the non-metallic properties of the stiffness device directlyresulting in a change of stiffness of the stiffness device to the stiffstate without straightening the catheter; physically contacting the RFenergy supply device with the treatment site; and delivering RF energyto the treatment site from the RF energy supply device.
 2. The methodaccording to claim 1, which further comprises gaining access to thetreatment site with the guidewire by steering the guidewire into placeusing radiographic guidance.
 3. The method according to claim 1, whichfurther comprises: placing the catheter into the relatively soft stateby changing a temperature of the stiffness device with thetemperature-changing device to at least approximately 115° F.; andplacing the catheter into the relatively stiff state by changing atemperature of the stiffness device with the temperature-changing deviceto approximately body temperature.
 4. A method for operating acontrollable stiffness catheter to treat atrial fibrillation, whichcomprises: providing a controllable stiffness catheter having: a shafthaving a distal end, a stiffness sheath, and an access lumen; a heaterinside the stiffness sheath; a non-metallic binder filling the stiffnesssheath containing the heater to at least partially surround andthermally contact the heater, the non-metallic binder being relativelysolid at or below body temperature and at least partially melting andrelatively softened above body temperature, the shaft being in arelatively stiff state when the binder is at or below body temperatureand in a relatively flexible state when above body temperature; a powerconnection selectively supplying power to the heater to change astiffness of the shaft between the relatively stiff state when theheater is not powered and the relatively flexible state when the heateris powered; and a radiofrequency (RF) energy supply device having atleast a portion disposed at the distal end of the shaft for selectivelysupplying RF energy from the distal end; applying power to the heater toplace the shaft in the relatively flexible state; traversing a passageof a body with the shaft in the relatively flexible state to deliver thedistal end of the catheter to a cardiac tissue treatment site and tophysically contact the RF energy supply device with the treatment site;removing power from the heater to place the catheter into the relativelystiff state and to substantially maintain a current shape of the shaftin the body and at least a portion of the distal end in contact with thetreatment site; and delivering RF energy to the treatment site from theRF energy supply device.
 5. The method according to claim 4, whichfurther comprises: placing the catheter into the relatively flexiblestate by changing a temperature of the heater to a first temperature;and placing the catheter into the relatively stiff state by changing atemperature of the heater to a second temperature different from thefirst temperature.
 6. The method according to claim 5, wherein the firsttemperature is higher than the second temperature.
 7. The methodaccording to claim 6, wherein the second temperature is approximately atbody temperature and the first temperature is at least 10 degreesFahrenheit greater than the second temperature.
 8. The method accordingto claim 6, wherein the second temperature is approximately 105° F. andthe first temperature is at least approximately 115° F.
 9. A method fordelivering a selectively articulated catheter to a treatment site, whichcomprises: extending a guidewire to a treatment site in a body;providing a controllable articulation catheter having: a shaft having astiffness sheath and an access lumen; an articulation control devicedisposed at the stiffness sheath and being in a non-articulating stateat or below a first temperature and being in an articulating state at orabove a second temperature, the articulation control device having anon-metallic binder that is at least partially melted during thearticulating state; a temperature-changing device in thermal contactwith the articulation control device, the temperature-changing devicechanging a temperature of the articulation control device at least frombelow the first temperature to above the second temperature; and a powercontroller electrically connected to the articulation control device andselectively supplying power to the temperature-changing device to changea stiffness of the articulation control device between thenon-articulating state and the articulating state; while supplying powerto the temperature-changing device to place the articulation controldevice in the articulating state: threading the catheter along theguidewire up to the treatment site; and pressing the catheter adjacentthe treatment site to articulate the shaft into at least one of adesired shape and a desired orientation; and removing power from thetemperature-changing device to place the articulation control device inthe non-articulating state without straightening the shaft and, thereby,substantially maintain at least one of the desired shape and theorientation of the shaft.
 10. The method according to claim 9, whichfurther comprises, with the catheter in the non-articulating state,distally extending the guidewire through the treatment site to create abreach at the treatment site.
 11. The method according to claim 10,which further comprises: withdrawing the catheter from the guidewirewhile leaving the guidewire in the breach; and advancing a secondprosthesis implanting catheter different from the catheter over theguidewire and through the breach to implant a prosthesis at thetreatment site.
 12. The method according to claim 11, wherein the secondprosthesis implanting catheter is a balloon expanding catheter and theprosthesis is a stent surrounding a balloon, and which further comprisesexpanding the balloon to dilate the treatment site and place the stentwithin the dilated breach.
 13. The method according to claim 11, whereinthe second prosthesis implanting catheter is a sheath delivery catheterand the prosthesis is a stent compressed within a sheath of the sheathdelivery catheter, and which further comprises withdrawing the sheath topermit expansion of the stent and dilation of the breach.
 14. The methodaccording to claim 9, wherein the treatment site is a Chronic TotalOcclusion.
 15. The method according to claim 9, which further comprises,with the catheter in the non-articulating state, entirely removing theguidewire and replacing the guidewire with a breaching tool and distallyextending the breaching tool through the treatment site to create abreach at the treatment site.
 16. The method according to claim 9, whichfurther comprises, with the catheter in the non-articulating state,sliding a tool distally over the catheter at a proximal end of thecatheter and extending the tool over the catheter to the treatment site.17. The method according to claim 9, which further comprises: providingat least a portion of a radiofrequency (RF) energy device at a distalend of the catheter for selectively supplying RF energy from the distalend; and after placing the catheter into the non-articulating state:physically contacting the RF energy device with the treatment site; anddelivering RF energy to the treatment site from the RF energy device.18. The method according to claim 9, which further comprises, afterplacing the catheter into the non-articulating state: traversing aradiofrequency (RF) energy device to a distal end of the catheter forselectively supplying RF energy from the distal end; and delivering RFenergy to the treatment site from the RF energy device.
 19. The methodaccording to claim 9, which further comprises, after placing thecatheter into the non-articulating state: removing the guidewire toempty the access lumen; traversing a radiofrequency (RF) energy deviceto a distal end of the catheter for selectively supplying RF energy fromthe distal end; physically contacting the RF energy device with thetreatment site; and delivering RF energy to the treatment site from theRF energy device.
 20. The method according to claim 9, which furthercomprises: before placing the catheter into the non-articulating state,traversing a radiofrequency (RF) energy device to a distal end of thecatheter for selectively supplying RF energy from the distal end; andafter placing the catheter into the non-articulating state, deliveringRF energy to the treatment site from the RF energy device.
 21. Themethod according to claim 9, which further comprises: before placing thecatheter into the non-articulating state: removing the guidewire toempty the access lumen; and traversing a radiofrequency (RF) energydevice through the access lumen to a distal end of the catheter forselectively supplying RF energy from the distal end; and after placingthe catheter into the non-articulating state: physically contacting theRF energy device with the treatment site; and delivering RF energy tothe treatment site from the RF energy device.